Not sure if this is your particular problem or not, but a friend of mine had the same issue a short time ago. His older Yamaha started dripping oil. He took it to our local boat dealer and the mechanic found the issue pretty quick. There is a oil (catch/overflow) box on those older engines that catch any excess oil and his had finally filled up over many years of use and it was running over. Mechanic emptied the box and cleaned everything up and no more oil drips. You might check yours out to see if that is the issue.